6 Principles of SmokingZdzisław E. Sikorski and Izabela SinkiewiczDepartment of Food Chemistry, Technology, and Biotechnology, GdanskUniversity of Technology, Gdansk, Poland
6.1 Introduction
Treatment of a large variety of foods with wood smoke has beenpracticed for centuries—predominantly meats, poultry, and fish, butalso scallops, cheeses, prunes, paprika, and the malt used to producewhiskey and some sorts of beer. The process usually includes saltingand partial drying; it may also be coupled with heating. The aim isto increase the shelf life of the products, prevent food poisoning,and add a desirable smoky flavor. Smoking is applied at both anindustrial scale in food plants and in traditional artisan processingin simple kilns. With the advent of canning, freezing, and therefrigeration chain, the preservative effect of smoking has graduallylost its importance. The process parameters required to obtain a verylong shelf life through smoking are very severe and may decreasethe nutritional value of a product and increase the health risks forthe consumer.
6.2 Wood-smoke composition
Smoke develops from the charring of wood: beech, oak, alder, hick-ory, or maple, as well as fruit trees. Pinewood is used only seldom. Toproduce the desirable flavor that is characteristic of some products,juniper berries or pinecones are added to the smoldering material.The wood usually takes the form of shavings or sawdust. Today, theseare available commercially in different assortments of standardizedmesh size and moistness. In old-type kilns and friction-type genera-tors, wood logs are also used.
The thermal decomposition of the woody material, followed byoxidation, generates hundreds of solid, liquid, and gaseous com-pounds, differing in boiling point, solubility, chemical properties,and the role they play in food smoking. These are mainly H2O,CO, CO2, alcohols, carbonyl compounds, carboxylic acids, esters,hydrocarbons, nitrogen oxides, and phenols. The yield of the variouscomponents depends on the species of wood and the smolderingparameters. Mixed with air, they form a complex aerosol. The massproportion of the dispersing and dispersed phases of the aerosoldepends on the chemical composition of the constituents and ontemperature: heating increases the concentration of componentsin the gaseous phase, while cooling causes many compounds to
condensate and so move in the form of tiny solid particles or liquiddroplets to the dispersed phase.
The phenolic fraction, about 240 items, contains mainly guaiacoland its derivatives, phenol, 2,5-dimethylphenol, cresols, syringol andits derivatives, pyrocatechins, resorcinol, pyrogallol, hydroquinone,and hydroxy-dimetoxyphenylo-ketones. The composition of thephenolic fraction depends on the temperature of smoke generation.Increasing the temperature decreases the content of syringol and4-methylguaiacol and the percentage of trans-isoeugenol. Thehighest yield of smoke phenols occurs in the temperature range480–520 ∘C. The smoke aldehydes and ketones are also numerous.Formaldehyde is generated by the oxidation of methanol, one ofthe main products of the dry distillation of wood. The group ofcarbonyl compounds includes inter alia acetaldehyde, benzalde-hyde, acetone, and furanone. The acid fraction contains mainlyacetic acid, other components being various short-chain carboxylicand ketocarboxylic acids. Among the alcohols are a variety oflow-molecular-weight aliphatic compounds. Several componentshave been identified also in the ester fraction.
The group of hydrocarbons comprises various aliphatic com-pounds and polycyclic aromatic hydrocarbons (PAHs). Wood smokecontains about 60 identified PAHs, differing in number of aromaticrings and structure, as well as in physical and biological properties.Among them are the following 16 potentially mutagenic and/orcarcinogenic ones: cyclopenta[cd]pyrene, benzo[a]anthracene,chrysene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene (BaP), benzo[ghi]perylene, dibenzo[ah]anthracene, dibenzo[ae]pyrene, dibenzo[ah]pyrene, dibenzo[ai]pyrene, dibenzo[al]pyrene, indeno[1,2,3-cd]pyrene, 5-methyl-chrysene, and benzo[c]fluorene. The structure of these compoundsdetermines their biological activity, because in the living organismthey are activated on different routes, which are catalyzed by variousenzymes. The concentration of PAHs in wood smoke dependsmainly on the temperature of the smoldering wood and on theaccess of air. Increasing the smoke-generation temperature leads toa larger proportion of the high-molecular-weight compounds in thetotal PAHs. The content of PAHs in the smoke can be minimizedby keeping the glowing temperature below 400 ∘C and removingthe tar.
Wood smoke can be condensed and purified, yielding variouspreparations. These are used for smokeless smoking of meats. The
39
40 Handbook of Fermented Meat and Poultry
concentration of PAHs in such preparations can be effectivelycontrolled. According to EU Directive 2065/2003, the BaP con-tent in smoke preparations must not exceed 10 ng/g (EuropeanParliament, 2003).
6.3 The preserving effect
Smoking of foods can be regarded as “hurdle technology”(Figure 6.1). Smoked products are not sterile. The preserving effectresults from the consecutive or simultaneous action of several of thefollowing factors: thermal inactivation of the spoilage microflora,water activity, pH, antibacterial activity of additives used prior tosmoking, concentration of antimicrobial and antioxidant smokecomponents in the product, barrier properties of the packing,and storage temperature. Therefore, the high-quality life and thepractical storage time of various smoked foods extends from afew days in refrigeration conditions to several months at roomtemperature, depending on the kind, initial freshness, microbialcontamination, and form of the raw material, on the parametersof salting and curing, on loss of water due to dripping or drying,temperature, duration, and smoke density in the smokehouse, andon the conditions of packaging and storage of the product.
Numerous components of wood smoke have antimicrobialactivity in concentrations similar to those found in smoked meats.Among the most active are various phenols, especially guaiacol andits derivatives, cresol, pyrocatechols, and pyrogallol. The contentsand distributions of the phenols and their derivatives in smokedmeats are related to their solubility in the lipid and water phases ofthe products, as well as to the smoking conditions. Mini-salamisin sheep casings, 18–20 mm in diameter, smoked for 30 minutesat 22 ∘C with smoldering smoke from beechwood chips, contain
from 30 to 72 μg/g of the sum of guaiacol, 4-methylguaiacol,syringol, eugenol, and trans-isoeugenol (Hitzel et al., 2012), whilehot-smoked frankfurter-type sausages contain 19.6–57.6 μg/g,depending on the process parameters (Pohlmann et al., 2012).Compounds with an additional aldehyde group in their structureare more effective antimicrobials than phenols. The sensitivity ofdifferent species and strains of microorganism towards variousphenols may significantly differ in broth and in smoked meatproducts. The growth inhibitory concentration of some smokephenols in broth towards Listeria monocytogenes is in the range of10–100 μg/g. However, as yet it is not possible to predict exactlythe concentration of total smoke phenols that is necessary for aninhibitory effect on, for example, L. monocytogenes or Clostridiumbotulinum in foods. Cold smoking may decrease the population ofL. monocytogenes on the surface of the products, but might also leadto proliferation of these bacteria in meats cured with contaminatedbrine. The growth of L. monocytogenes has been shown in variousready-to-eat smoked products.
Smoke carbonyl compounds, especially formaldehyde, are alsoknown to retard the proliferation of microorganisms. Smoked meatsmay contain up to 125 μg/g formaldehyde. Most sensitive are thevegetative forms of bacteria; molds and yeasts are more resistant.Many molds were isolated from fully ripened, lightly smokedNorwegian dry-cured meats, and the predominant species werefound to belong to the genus Penicillium (Asefa et al., 2009).
Generally, smoke components alone cannot protect lightly smokedfoods from spoilage and microbial hazards for long. At the concen-trations found in foods, the smoke constituents do not decrease thepopulation of various pathogenic microorganisms by several logcycles, or efficiently restrain their growth. A significant antilisterialeffect can be achieved by adding potassium lactate and sodiumdiacetate to the sausage formulation and by 2 minutes’ immersion
12
3
4
5
67
8
9
10
11
Time of storage
Log
num
ber
of b
acte
ria /
g
Figure 6.1 Effect of preservative treatments on the growth of bacteria in foods: (1) untreated food, room temperature; (2) refrigeration; (3) chemical preser-vation and refrigeration; (4) chemical preservation, modified atmosphere, and refrigeration; (5) drying or salting, room temperature; (6) marination or lacticacid fermentation, room temperature; (7) drying or salting and refrigeration; (8) freezing; (9) heat pasteurization, room temperature; (10) heat pasteurizationand chemical preservation, room temperature; (11) heat pasteurization and refrigeration.
6 Principles of Smoking 41
OH O OO
O O
.LOO
.
.
+ LOOH +
.
.
LOO +.
R4
R4
R4 R4 R4R4
R2 R2
R2R2R2R2
R6 R6
R6 R6 R6R6
OOL
Figure 6.2 Mode of action of a phenolic antioxidant.
of the smoked sausages in various antimicrobial solutions. Sprayingfrankfurters with liquid smoke of pH 4.25–4.85, containing in1 cm3 0.3–0.8 mg of phenols, decreased the surface populationof L. monocytogenes during storage at 4 ∘C by several log cycles(Martin et al., 2010). In a particular smoked product type, the effecton the bacterial population depends on all factors involved in thehurdle technology and on the implementation of the food safetymanagement system.
Smoking also prolongs the shelf life of foods by decreasing the rateof lipid oxidation, mainly due to the antioxidant activity of variousphenols. The phenolic antioxidants are capable of inactivating differ-ent free radicals present in the products by donating the hydrogenatom of the OH group and thus breaking the chain reaction of lipidautoxidation (Figure 6.2). A phenolic radical created by abstractionof the hydrogen atom has a lower reactivity than other free radicals,as a result of the resonance delocalization of the radical functionin the aromatic structure. The activity of the phenol antioxidantincreases with decreasing binding energy of the hydrogen atomin the OH group and decreasing energy of the created phenolicradical. Both of these characteristics depend on the structure ofthe compound, which explains why various smoke phenols differin antioxidant effect. The activity of several smoke componentsexceeds that of the known food additives buthylhydroxyanisole(BHA) and buthylhydroxytoluene (BHT). The most effective areresorcinol, pyrogallol, 4-methylguaiacol, 4-vinylguaiacol, andtrans-4-propenylsyringol. The protective action of smoking dependstoo on the presence in food of various compounds that decreasethe activity of the antioxidants or act synergistically on the factorsinfluencing the rate of formation of reactive oxygen species (ROS),as well as on the distribution of lipids in the product. Thus, completearrest of lipid changes is not possible, and various compoundsgenerated due to thee oxidation of polyenoic fatty acids occurin smoked meat, among them minute amounts of the cytotoxicaldehyde 4-hydroxy-2-nonenal.
6.4 The flavoring effect
6.4.1 IntroductionThe sensory properties of smoked foods depend on the type of prod-uct, its initial quality, the preparation of the raw materials prior tosmoking, loss of moisture and thermal changes during processing,and the concentrations of various smoke components on the surface
and in the deeper layers of the product. The color, flavor, and tastetypical of smoked meats and fish are formed by the smoke com-pounds, while the texture, juiciness, and saltiness result from theproperties of the raw material and the processing parameters.
6.4.2 ColorThe color of the surface of smoked foods is a blend of the pigmen-tation of the raw material and that resulting from the action of thesmoke components. The tint added by smoking extends from lightlemon to dark brown, depending mainly on the kind of smolderingwood and the time/temperature regime of the process. It is espe-cially visible on the carcasses of poultry and the originally whitishor silvery belly parts of fish, while on many sausages and other meatproducts a red coloration predominates.
The color added by smoking is a result of the deposited coloredsmoke components, their changes during heating and storage,and their interactions with the surface material of the product.The chemical changes involved comprise mainly polymerizationof phenols and the Maillard reaction; their rate increases withtemperature. Thus, raising the smoke temperature promotes darkercolorization of the products. Most important is the amount ofdeposited smoke components. Heavily smoked goods—that is,those kept in a dense smoke for a long time—turn very dark brown.This color can also develop on surfaces containing no componentscapable of interacting with the reactive smoke compounds. The tintis also affected by the characteristics of the sawdust taken for smokegeneration; using beech, maple, ash, sycamore, or lime tree shavingsfavors a golden-yellow color, while oak, nut, and alder smokes causeyellow-brownish coloration, and meats treated with smoke fromconiferous wood have a dark coloration. Consumer preferencesregarding the color of various smoked meat products are not equalin different regions.
6.4.3 Flavor and tasteThe smoky flavor is created mainly by the smoke componentsdeposited on the product, predominantly the phenols. The com-pounds that contribute to the formation of the desirable flavorare mainly syringol, 4-methylsyringol, 4-allylsyringol, guaiacol,4-methylguaiacol, and trans-isoeugenol. Carbonyl compounds,furans, and other smoke constituents play a role as well, althoughthe exact proportions of the concentrations of different smokecomponents in the creation of various flavor notes have not beendisclosed.
42 Handbook of Fermented Meat and Poultry
Smoke phenols, aldehydes, and acids interact with different foodcomponents. This may affect the sensory qualities of the products.
6.5 Benefits and risks
6.5.1 IntroductionThe intended, desirable effects of smoking comprise first the forma-tion of the typical sensory properties of the products—attractive fea-tures are added to smoked foods, which are highly valued by manyconsumers—and second, the prolonged storage life of the product,brought about by the prevention of the growth of some microorgan-isms, including pathogens, and by the delay of lipid oxidation.
Smoked foods may contain microbial toxins carried through fromthe raw material or generated by microflora that survive the pro-cessing and are active in the product during storage. They may alsoharbor excessively large populations of pathogenic microorganisms.The hazards that can be caused by pathogenic microflora dependon the initial contamination of the raw materials, on the lethal andgrowth-inhibitory effects of the processing procedure, and on thehandling and storage parameters of the products.
Further risks are caused by certain smoke components depositedon the meats and the effects of their interactions with the productconstituents. Most smoke compounds would not be allowed by lawto be added to foods in pure form; however, as their toxicity andconcentration in these products are very low, smoking is generallyregarded as safe (GRAS), in accordance with the common law prin-ciple De minimis non curat lex.
6.5.2 PAHsThe smoke components that are hazardous to consumer health andwhose content in smoked foods is limited by law are the PAHs.The mutagenic/carcinogenic activities of ingested individual PAHs,as well as their concentrations, are different in various smokedfoods. Thus, it is very difficult to predict the degree of health hazardcaused by these compounds in smoked foods. Various PAHs havebeen proposed as indicators of carcinogenicity. Until recently,BaP was regarded as such, since it is a very potent mutagenic andcarcinogenic compound. This indicator is, however, not generallyaccepted anymore, as some smoked goods contain a large number ofother highly carcinogenic PAHs and no BaP. On the other hand, thecontent of BaP in many different smoked meat products has beenfound to be highly correlated with that of most other carcinogenicPAHs (Lorenzo et al., 2011). According to a statement by theEuropean Food Safety Authority (2008), a more adequate index ofthe carcinogenicity of smoked foods is the sum of the concentrationof BaP, benzo(a)anthracene, benzo(b)fluoranthene, and chrysene(PAH4) (Figure 6.3), or else the concentration of eight carcino-genic PAHs (PAH8): the PAH4 plus benzo[k]fluoranthene, benzo[g,h,i]perylene, dibenzo[a,h]anthracene, and indeno[1,2,3-cd]pirene. However, because most earlier published data on PAHs insmoked foods regarded the content of BaP, Commission Regulation(EU) No. 835/2011 (European Commission, 2011) decided tokeep the maximum level of this indicator in smoked meat and meatproducts at 5 ng/g until August 2014, and at 2 ng/g afterwards. Addi-tionally, an upper limit of 30 ng/g for PAH4 has been introduceduntil August 2014, and 12 ng/g afterwards.
benzo(a)pyrene benzo(a)anthracene
benzo(b)fluoranthene chrysene
Figure 6.3 The four polycyclic aromatic hydrocarbons (PAH4) treated as anindex of the carcinogenicity of smoked foods.
The content of PAHs in smoked meat products available on themarket is usually well below the maximum level set by the EU. Thelimits of quantification of individual PAHs achievable by contempo-rary analytical procedures range from 0.009 to 0.030 ng/g (Jira et al.,2008). Various assortments of smoked meats usually contain nomore than 1 ng BaP/g, although very heavily smoked products mayreach up to 50 ng BaP/g. Meat products manufactured by traditionalSwedish “sauna” smoking involving direct exposure to hot smokegenerated by a flaming log fire were found to contain 6.6–36.9 ngBaP/g (Wretling et al., 2010). Market samples of smoked meatsin Kuwait contained 0.97–1.20 ng BaP/g, 3.26–7.45 ng PAH8/g,and 82.9–110.0 ng total PAHs/g (Alomirah et al., 2011). Accordingto different published data on about 600 smoked meat products,the contents of BaP, PAH4, and PAH8 were about 0.20, 1.5, and1.8 ng/g, respectively. The concentration of 16 PAHs in 22 samplesof smoked ham ranged from below 0.01 to 19 ng/g, with the medianfor BaP being below 0.15 ng/g (Jira et al., 2008). In the raw-curedSpanish pork sausages androlla and botillo, smoked 8–10 and7–15 days, respectively, in traditional kilns and ripened for severalmonths, the mean contents of the 16 potentially mutagenic and/orcarcinogenic PAHs were 36.5 and 29.4 ng/g, respectively, in whichthe BaP content ranged from 15 to 17% (Lorenzo et al., 2010).
The accumulation of PAHs in different smoked meat products isrelated very significantly to the parameters of smoking and the kindof wood used for smoke generation. Assortments of sausages madeof various raw materials, although having the same mass to surfaceratio and being smoked in identical conditions, contain differentamounts of PAHs (Roseiro et al., 2012). In traditionally smokedsausages, the PAHs content depends even on the location of theproduct in the kiln, which affects the temperature and flow rate ofthe smoke. Meat products treated with smoke made from the woodof apple tree and alder contained about 10 times less total PAHsthan samples smoked in the same conditions with spruce smoke(Stumpe-Vıksna et al., 2008). Generally, the PAHs contaminationof products smoked in strictly controlled conditions in modernsmokehouses with external smoke generators is significantly lowerthan that of meats processed in old-type kilns with smolderingchips or burning wood logs directly under the hanging rows of
6 Principles of Smoking 43
sausages. The inner parts of the products are less contaminated thanthe surface layers, although during storage this difference graduallydiminishes. The skin is an effective barrier for PAHs; this applies forvarious smoked fish, especially eel, and has been shown to hold forbacon smoked with skin versus that without (Djinovic et al., 2008).
The concentration of PAHs in smoked products changes duringstorage. Being hydrophobic, they accumulate in fatty tissues at arate controlled by the parameters of diffusion. They may also beabsorbed by low-density polyethylene packaging films and therepartially destroyed by UV radiation (Chen & Chen, 2005; Šimko,2005). The photochemical changes induced by UV involve oxidationof peripheral carbons, leading to aromatic alcohols, ketones, andethers.
6.5.3 Other hazardous compoundsThe reactions of various smoke constituents with the components offoods may result in the formation of different groups of hazardouscompounds. Smoking, as applied in the manufacture of the smokeddry-cured ham prosciutto di Sauris (2–3 days at 20 ∘C), has beenfound to have only a very limited effect on protein hydrolysis andthe accumulation of biogenic amines in the meat (Martuscelli et al.,2009).
Several heat-treated foods may contain nitropolycyclic aromatichydrocarbons in concentrations of up to about 30 ng/g. In smokedsausages, the contents of 1-nitropyrene, 2-nitronaphtalene, and2-nitrofluorene have been found to be in the range of about4–20 ng/g
N-nitroso compounds, most of which are carcinogenic in labora-tory animals, may be formed in smoked foods by the reaction ofsmoke aldehydes with cysteamine and cysteine, yielding various thi-azolidine precursors that can be easily nitrosated. In various smokedmeat and poultry products, the contents of N-nitroso compoundsmay reach up to several hundreds of ng/g.
Heterocyclic aromatic amines, known to be generated in pyrolyticreactions of amino acids and proteins and in non-enzymatic brown-ing, are present in very heavy smoked goods in amounts lower than1 ng/g.
In various smoked foods, β-carboline alkaloids are also found.These may be formed in the reaction of L-tryptophan withformaldehyde or acetaldehyde (see Figure 6.4). The concen-tration of these compounds increases with temperature andduration of smoking, and depends on the accumulation offormaldehyde with the smoke. In sausages, 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THCA) is found in concentrationsof 0.01–14.80 μg/g. The outer surfaces of smoked products maycontain up to eight times more THCA than the core (Papavergou &Herraiz, 2003).
6.6 Food engineering approach
6.6.1 Mass and heat transferThe aim of meat smoking is to achieve a desirable product qualitythrough the action of the smoke and heat and the loss of moisture.The smoke constituents settle on the meat, driven by gravitationaland centrifugal forces, and are absorbed in the thin film of water onthe surface. The rate of deposition of various compounds depends onwhether they are in the dispersing or dispersed phase of the aerosolat the given temperature and on the condition of the surface layer(Miler & Sikorski, 1990). Therefore, the temperature, humidity, andflow rate of the smoke significantly affect the efficiency of the sorptionphenomena. These factors control the absorption of smoke compo-nents in conventional smoking, as well as in smokehouses suppliedwith dispersed, atomized smoke preparations. If the preparations areused in the form of dips, the process is governed by the laws of dif-fusion. In electrostatic smoking (Figure 6.5), the decisive factor isthe electrostatic force, which drives the electrically charged smokeparticles towards the product and creates an electric wind to carrythe uncharged components of the aerosol in the same direction.
2 6
5
‒30 kV
3
4
1
Figure 6.5 The principle of electrostatic smoking: (1) smoke inlet; (2)smoked sausage; (3) metallic, grounded conveyer chain; (4) smoke outlet;(5) insulator; (6) ionizing electrode. Source: Courtesy of Łukasz Wisniewski.
Figure 6.6 Traditional smoking kiln. Source: Courtesy of ŁukaszWisniewski.
The temperature, humidity, and flow rate of smoke/air also influ-ence the rate of loss of moisture from the smoked meats, as well asthe heat transfer by convection and by condensation of water vaporon the cool surface of the product in the early stage of smoking.
6.6.2 EquipmentIn artisanal manufacturing of smoked foods, the sensory, nutri-tional, food-safety, and economic requirements are fulfilled by atrained craftsperson, who knows by experience how to processa given raw material using the available wood and equipment atthe prevailing atmospheric conditions. Artisan smoking usuallytakes place in kilns, in which logs of wood burning on the floorand smoldering shavings or sawdust supply the necessary heat andsmoke (Figure 6.6). The meat to be smoked is hung on racks atdifferent heights above the fireplace. The conditions prevailing invarious locations in the kiln differ significantly; therefore, it may benecessary to reverse the racks of sausages during the process. Thetemperature, density, and humidity of the smoke are controlled tosome degree by the operator, by way of the proper use of the moist ordry woody material and by opening and closing the vent and doors.
In order to produce high-quality smoked meats at commercialscale, contemporary requirements regarding the standard of the rawmaterial, precisely defined and strictly applied processing param-eters, rational equipment design, and proper organization of themanufacturing line should be observed. Furthermore, procedureseliminating health risks should be introduced, such as the hazardanalysis and critical control points (HACCP) system.
In modern smokehouses containing production lines, foodengineering principles are applied to implement rational param-eters of mass and heat transfer and to achieve organizational andeconomic goals.
Figure 6.7 Modern smokehouse. Source: Courtesy of Łukasz Wisniewski.
Wood smoke is produced in outside generators, often filtered toseparate the tar and soot, and directed into the smokehouse by ducts.Mostly smoldering-type units are used, in which the woody materialis fed automatically on an electrically heated plate or grate. The tem-perature in the smoldering pile of sawdust can be kept at a level of400–600 ∘C by changing the flow rate of the air and the humidity ofthe woody material.
Less common are various types of machine in which the smokedevelops due to heat generated as a result of friction from a woodlog pressed against a rotating metal ring or disk. By adjusting thepressure exerted on the log or the rotation rate of the disk, the tem-perature at the friction interface can be controlled; it is usually kept atabout 400 ∘C. An asset of this type of generator is that smoke devel-ops immediately after the drive engine is switched. They are noisy,however.
Several other types of machine can produce smoke at relatively lowtemperature. In one such unit, the smoke is developed by treating thewoody material with overheated steam at about 250–390 ∘C.
Modern smokehouses are usually built in the form of kilns, tun-nels, or towers (Figure 6.7). They work either periodically or contin-uously. The smoke is distributed evenly and circulated at controlledvelocity by the action of fans and shutters. Smokehouses used to treatmeats with smoke preparations are additionally equipped with noz-zles or evaporating heated plates to turn the liquid preparation intoan aerosol. The necessary heat is supplied by steam, gas, or electric-ity. The smoke temperature, density, and humidity and the smokingtime are adjusted according to a program set for the particular prod-uct to be processed. In the manufacture of many types of smokedsausage, the smoking phase is followed by a period of cooking undera hot-water shower or by steam. The sausages to be smoked are hungon rods and transported into the smokehouse on trolleys, movingeither on the floor or on an overhead track. In tower smokehouses,the goods are moved vertically on a chain transporter.
The spent smoke leaving the smokehouse carries many atmo-spheric pollutants and should be cleaned. This can be done by
6 Principles of Smoking 45
different kinds of filter or afterburner. To avoid accumulation oftars, which contain more PAHs than the smoke, and to preventthe outbreak of fire, many smokehouses have automatic cleaningsystems.
6.7 Smoking procedures
A number of smoking procedures have been developed in thelast several centuries, suitable for treating various commodities.They differ in the mode of preparation of the raw material and inthe parameters of treatment in the smokehouse—mainly smokehumidity and temperature, as well as the duration of the process.
Smoking usually constitutes one of a chain of several unit oper-ations and unit processes in the manufacture of a meat product.Depending on the intended characteristics of the product, a suitableraw material and pretreatment are selected, cold, warm, or hotsmoking is applied, and different methods of heating are used (e.g.,warm air, steam cooking, or cooking in water). Cold smoking, ata temperature of 12–25 ∘C, lasts from a few hours to several days.It is typical in the manufacture of raw fermented sausages madeof cured meat, some assortments produced from variety meats,and pork belly. The parameters of fermented sausage smokingshould promote the proliferation of lactic acid bacteria (LAB),ensure the predetermined loss of moisture, and lead to specific,rheological properties in the product. Warm smoking, at 25–45 ∘C(i.e., in conditions under which the fats in the batter change theirconsistency but no protein denaturation occurs), usually lasts up toa few hours. It is normal in the manufacture of baked or scaldedsausages, pork back fat, and hams. Hot smoking is carried outat 45–90 ∘C. Depending on the assortment of sausage, it may beapplied at several stages of the manufacturing process, and it canlast from a few hours up to 12. It leads to the development of smokysensory characteristics, thermal denaturation of proteins, and apredetermined yield of product.
References
Alomirah H, Al-Zenki S, Al-Hooti S, Zaghloul S, Sawaya W, Ahmed N,Kannan K. 2011. Concentrations and dietary exposure to polycyclicaromatic hydrocarbons (PAHs) from grilled and smoked foods. FoodControl, 22(11), 2028–2035.
Djinovic J, Popovic A, Jira W. 2008. Polycyclic aromatic hydrocarbons(PAHs) in different types of smoked meat products from Serbia. MeatScience, 60(2), 449–456.
European Commission. 2011. Commission Regulation (EU) No 835/2011 of19 August 2011 amending Regulation (EC) No 1881/2006 as regards max-imum levels for polycyclic aromatic hydrocarbons in foodstuffs. OfficialJournal of the European Union, 20, 8, L215/6-L215/8.
European Food Safety Authority. 2008. Polycyclic aromatic hydrocarbons infood: scientific opinion of the panel on contaminants in the food chain.EFSA Journal, 724, 1–114.
European Parliament. 2003. Parliament and Council Regulation (EC) No.2065/2003 of 10 November on smoke flavourings used or intendedfor use in or on food. Official Journal of the European Union, L 309,26/11/2003/1-8.
Hitzel A, Pöhlmann M, Schwägele F, Speer K, Jira W. 2012. Polycyclicaromatic hydrocarbons (PAH) and phenolic substances in cold smokedsausages depending on smoking conditions using smoldering smoke.Journal of Food Research, 1(2).
Chen J, Chen S. 2005. Removal of polycyclic aromatic hydrocarbons by lowdensity polyethylene from liquid model and roasted meat. Food Chem-istry, 90, 461–469.
Jira W, Ziegenhals K, Speer K. 2008. A GC/MS method for the determina-tion of 16 European priority polycyclic aromatic hydrocarbons in smokedmeat products and edible oils. Food Additives and Contaminants, 25(6),704–713.
Lorenzo JM, Purriños L, Fontán MC, Franco D. 2010. Polycyclic aromatichydrocarbons (PAHs) in two Spanish traditional smoked sausage varieties:“Androlla” and “Botillo.” Meat Science, 86(3), 660–664.
Lorenzo JM, Purriños L, Bermudez R, Cobas N, Figueiredo M, GarcíaFontán. 2011. Polycyclic aromatic hydrocarbons (PAHs) in two Spanishtraditional smoked sausage varieties: “Chorizo gallego” and “Chorizo decebolla.” Meat Science, 89(1), 105–109.
Martin EM, O’Bryan CA, Lary RY Jr, Griffis CL, Vaughn KL, Marcy JA, RickeSC, Crandall PG. 2010. Spray application of liquid smoke to reduce oreliminate Listeria monocytogenes surface inoculated on frankfurters. MeatScience, 85(4), 640–644.
Martuscelli M, Pittia P, Casamassima LM, Manetta AC, Lupieri L, Neri L.2009. Effect of intensity of smoking treatment on the free amino acids andbiogenic amines occurrence in dry cured ham. Food Chemistry, 116(4),955–962.
Miler KMB, Sikorski ZE. 1990. Smoking. In: Seafood: Resources, NutritionalComposition, and Preservation. ZE Sikorski (ed.), pp. 163–180. BocaRaton, FL: CRC Press.
Papavergou E, Herraiz T. 2003. Identification and occurrence of1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid: the main β-carbolinealkaloid in smoked foods. Food Research International, 36(8), 843–848.
Pohlmann M, Hitzel A, Schwagele F, Speer K, Jira W. 2012. Contents ofpolycyclic aromatic hydrocarbons (PAH) and phenolic substances inFrankfurter-type sausages depending on smoking conditions using glowsmoke. Meat Science, 90(1), 176–184.
Roseiro LC, Gomes A, Patarata L, Santos C. 2012. Comparative survey ofPAHs incidence in Portuguese traditional meat and blood sausages. Foodand Chemical Toxicology, 50(6), 1891–1896.
Šimko P. 2005. Factors affecting elimination of polycyclic aromatic hydro-carbons from smoked meat foods and liquid smoke flavorings. MolecularNutrition and Food Research, 49, 637–647.
Stumpe-Vıksna I, Bartkevics V, Kukare A, Morozovs A. 2008. Polycyclic aro-matic hydrocarbons in meat smoked with different types of wood. FoodChemistry, 110(3), 794–797.
Wretling S, Eriksson A, Eskhult GA, Larson B. 2010. Polycyclic aromatichydrocarbons (PAHs) in Swedish smoked meat and fish. Journal of FoodComposition and Analysis, 23(3), 264–272.
